Plan for security team review

Hi @dfinity/product-security — we'd like your input on this PR before it merges. Here's the context and what we're asking.

What this PR does

This is a 1:1 port of all security best practices from dfinity/portal (building-apps/security/) to this site. The primary goal was to replace AI-generated rewrites that had diverged from the carefully reviewed portal content, including a confirmed correctness bug (double-spend scenario in inter-canister-calls.md).

The only intentional deviations from a pure port are:

• 4 slug renames for SEO clarity (access-management → identity-and-access-management, misc → miscellaneous, etc.) — old URLs were broken anyway since the section was new
• resources.md merged into overview.md as a "Further reading" section (thin standalone page, no content lost)
• encryption.mdx removed — it was AI-generated and had never been security-reviewed; a proper vetKeys encryption guide will be written separately from the vetkd icskill
• Motoko CallerGuard updated from mo:base/HashMap to mo:core/Map (library migration required by project rules, not a security change)

You are now added as CODEOWNER for all files in docs/guides/security/, docs/concepts/security.md, docs/references/message-execution-properties.md, and docs/guides/canister-calls/idempotency.md. Your approval is required for any future changes to these files.

What we're asking from you

Please verify the ported content is correct and matches the portal source. We're keeping this PR in draft intentionally — it will not be merged until after a second cleanup PR (described below) is also approved.

What comes next — cleanup PR

After your approval of this PR, we'll create a second branch from docs/security-port to address editorial issues that go beyond the 1:1 port. We'd need your approval on that one too before anything merges to main. Known items for that cleanup:

1. Broken external link: https://www.joachim-breitner.de/blog/788-How_to_audit_an_Internet_Computer_canister — site is down (ECONNREFUSED). Appears 9 times across 6 files. We need to decide: find a replacement URL, point to a web archive, or remove the references.

2. Deprecated example link: decentralization.md links to https://github.com/dfinity/examples/tree/master/rust/basic_dao — this example no longer exists in the examples repo.

3. Outdated JS SDK references: data-integrity-and-authenticity.md imports from @dfinity/agent and identity-and-access-management.mdx links to agent-js — these should be updated to the current @icp-sdk/* packages.

4. Brand guideline violations: "dapps", "smart contracts", ... appear throughout, particularly in decentralization.md and overview.md. We'll align with current terminology in the cleanup — though we'd appreciate your input on whether any of these are load-bearing technical terms in the security context that should be preserved.

5. ICP Wiki links: 4 files link to wiki.internetcomputer.org, which is unmaintained and no longer the source of truth:

   • data-storage.md, canister-upgrades.md, inter-canister-calls.md (×2) — all pointing to "Current limitations of the Internet Computer" (covering pre_upgrade bugs, malicious callees preventing upgrades, loops in call graphs)
   • decentralization.md — "Verification and trust in a (launched) SNS" and "SNS decentralization swap trust"

   These will need to be replaced with links to current docs or the content inlined directly. Security team input welcome on where the canonical replacement should be, particularly for the "current limitations" page which is referenced 3 times.

Merge sequence

1. Your approval of PR docs(security): port security best practices 1:1 from portal #204 (this PR) → stays in draft
2. Cleanup branch → PR targets docs/security-port → your approval → merge into docs/security-port
3. Un-draft and merge PR docs(security): port security best practices 1:1 from portal #204 into main